1. Field of the Invention
The present invention relates to a method for operating a waste heat boiler in copper flash-smelting works, and more particularly to a technique for preventing accretion build-up by reducing the quantity of dust accretion to the water tube laid within the waste heat boiler in the flash-smelting furnace.
2. Description of the Related Art
In copper flash-smelting works, copper sulfide concentrate is fed with oil within the flash-smelting furnace and undergoes a gas phase reaction with air or oxygen. Dust carried over dispersed during this smelting process adheres to the water tube of the waste heat boiler in the flash-smelting furnace and reduces the steam yield of the boiler, thereby decreasing the waste heat recovery capacity of the boiler. Moreover, the waste heat boiler in the flash-smelting furnace has the function of recovering and utilizing waste heat attained by the cooling of the high temperature off-gas, including dust exhausted by the flash-smelting furnace; the waste heat boiler in the flash-smelting furnace contains a water tube for recovering waste heat.
In order to resolve the above-mentioned problem, a method was proposed wherein the forced oxidation of the dust is suppressed by feeding nitrogen gas into the waste heat boiler in the flash-smelting furnace, so as to make the dust build-up to the water tube of the waste heat boiler in the flash-smelting furnace unable to soften and be easily removed; furthermore, the dust accretion to the water tube of the waste heat boiler is suppressed by cooling the gas within the furnace and generating turbulence in the gas in the boiler (See Japanese Patent Laid-open No. 6-347001).
By blowing in nitrogen gas with an oxygen concentration of 2% according to the first embodiment in Japanese Patent Laid-open No. 6-347001, the gas temperature at the outlet of the waste heat boiler in the flash-smelting furnace was 30.degree. C. less than before gas was blown in; the amount of accretion to the water tube of the waste heat boiler was reduced and hardening was alleviated.
Also, according to the second embodiment of the above-mentioned citation, in the case of a low extraction rate at sulfuric acid leach of dust recovered with an electrostatic precipitator, the unsulfated dust was oxidized or sulfated, made into red, non-sticky dust, and easily leached by blowing in nitrogen gas with an oxygen concentration of 5% and increasing the partial pressure of oxygen within the waste heat boiler.
However, with the method in the above-mentioned citation, it was found that there were some cases when the accretion to the water tube of dust generated during actual operations could not necessarily be sufficiently suppressed. It is impossible to reduce dust accretion to the water tube because of volatile elements such as lead and zinc included in the ore. It would therefore be desirable to develop a technology which can further reduce the dust generation and more effectively prevent the dust accretion built-up to the water tube.